1. Field of the Invention
The present invention relates generally to a method and apparatus for troweling or screeding concrete and more specifically to an apparatus for screeding a poured concrete surface having a rigid frame structure and a telescopic boom that is secured directly thereto, said telescopic boom constructed to include a leveling system to maintain each section of the boom level with each preceding section thereof eliminating the need for continuous leveling controls, thereby providing a superior level finished surface.
2. Description of the Related Art
In the construction industry when liquid concrete is poured to produce a finished level surface it must be carefully leveled and smoothed, or screeded, so that when the concrete sets it produces an even, level surface. Since this level surface is almost always a foundation for additional construction, machine base applications, or for vertical storage such as warehousing space, it is highly desirable to produce a surface that is consistently level over its entire area. In large poured areas it is unwieldy and labor intensive to manually level and smooth a poured surface as well as extremely difficult to maintain a consistent finished grade.
In order to aid in the screeding of large surface area concrete pours, a variety of screeding or troweling machines have been accepted into use in the art. These machines typically include a screed head comprising a flat troweling surface for contacting the poured concrete mounted on a boom that is mechanically extended and retracted across the concrete surface to produce a smooth finish thereon. Many of these prior art devices include various systems for leveling the screed head relative to a reference plane such that the finished surface is relatively flat once it is screeded.
The leveling systems in prior art devices may encompass laser eyes mounted on the screed head structure that detect a laser beam projected at a predetermined level reference height above grade. Thus the screed head may be adjusted to a predetermined grade level by aligning said laser eyes with a projected laser beam. Furthermore, many of these devices provide automated means for adjusting the screed head upwardly or downwardly to a level reference plane, thus obviating the need for manual alignment. In some systems, the automated adjustment of the screed head requires the use of multiple sensors and actuators along with the concomitant wiring and computerized control systems required to effect the necessary leveling adjustments.
Prior art screeding devices often comprise a frame having a centrally mounted turret from which a boom is extended. One such system is disclosed in U.S. Pat. No. 5,039,249 to Hansen et al. Turret type screeders provide for some maneuverability since the turrets are capable of rotation via a driven gear or similar mechanism. These screeding systems are typically quite complex and costly due to the need for complicated mechanical and electrical controls not to mention the power required to position a turret. In fact, while many prior art screeding devices are available, a great deal of concrete screeding is still accomplished by hand due to the size and cost of automated screeders.
Additionally, turret-type systems, while providing for consistently level finished surfaces are extremely complex in terms of mechanical construction and control systems required for operation since they necessarily have a boom that extends from a central point of attachment to the screeder. In order to withstand the rigors of continuous use in construction environments, booms are typically comprised of a metal alloy which makes them quite heavy. As a result, when the boom is fully extended outwardly from the turret, there is some variation in the level of the screed head since a great deal of weight is secured to a single point of the screeding apparatus, namely the turret.
Another disadvantage in prior art screeding systems is the inability to level the boom relative to the screed head and the frame or body of the system. In many prior art devices, a plurality of legs or outriggers are provided to level the frame of the apparatus, and then the screed head is set to an appropriate finish grade height using the laser leveling process previously discussed. These systems typically approximate leveling the boom with respect to the frame in order to bring the screed head within a predetermined level tolerance for operational purposes. However, there remains a great deal of play or “slop” in the leveling process due to the size and weight of the boom and it's attachment to the screeder frame.
Accordingly, there is a need in the art for a system and method screeding and troweling concrete that provides a consistently level finished surface with a minimum of mechanical and electrical system complexity.